β Decays as Sensitive Probes of Lepton Flavor Universality

Crivellin, Andreas; Hoferichter, Martin (2020). β Decays as Sensitive Probes of Lepton Flavor Universality. Physical review letters, 125(11), p. 111801. American Physical Society 10.1103/PhysRevLett.125.111801

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Nuclear β decays as well as the decay of the neutron are well-established low-energy probes of physics beyond the standard model (SM). In particular, with the axial-vector coupling of the nucleon gA determined from lattice QCD, the comparison between experiment and SM prediction is commonly used to derive constraints on right-handed currents. Further, in addition to the CKM element
Vus from kaon decays, Vud from β decays is a critical input for the test of CKM unitarity. Here, we point out that the available information on β decays can be reinterpreted as a stringent test of lepton flavor universality (LFU). In fact, we find that the ratio of Vus from kaon decays over Vus from β decays (assuming CKM unitarity) is extremely sensitive to LFU violation (LFUV) in W−μ−ν couplings thanks to a CKM enhancement by (Vud/Vus)2∼20. From this perspective, recent hints for the violation of CKM unitarity can be viewed as further evidence for LFUV, fitting into the existing picture exhibited by semileptonic B decays and the anomalous magnetic moments of muon and electron. Finally, we comment on the future sensitivity that can be reached with this LFU violating observable and discuss complementary probes of LFU that may reach a similar level of precision, such as Γ(π→μν)/Γ(π→eν) at the PEN and PiENu experiments or even direct measurements of W→μν at an FCC-ee.

Item Type:

Journal Article (Original Article)

Division/Institute:

10 Strategic Research Centers > Albert Einstein Center for Fundamental Physics (AEC)
08 Faculty of Science > Institute of Theoretical Physics

UniBE Contributor:

Crivellin, Andreas and Hoferichter, Martin

Subjects:

500 Science > 530 Physics

ISSN:

0031-9007

Publisher:

American Physical Society

Language:

English

Submitter:

Esther Fiechter

Date Deposited:

19 Nov 2020 17:21

Last Modified:

21 Nov 2020 04:56

Publisher DOI:

10.1103/PhysRevLett.125.111801

ArXiv ID:

2002.07184

BORIS DOI:

10.7892/boris.148301

URI:

https://boris.unibe.ch/id/eprint/148301

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